Trunking communication is an important branch of wireless communication, which is mainly used in the field of professional mobile communication. The most important character of trunking communication is that the voice communication is performed in a manner of half-duplex, connected in a manner of push to talk, wherein the called user may answer the call without off-Hook, and a high connection speed is demanded. Out of optimization on trunking communication markets, digital trunking communication systems developed by communication manufacturers has come into entering this field, and relevant standards are issued one after another, and national standards for trunking communication develop in a “trunking” state in a period of time.
In a trunking communication system based on CDMA, CDMA technology is combined with a private scheduling communication system, and the communication manner of half-duplex is adopted, so that a quick connection can be carried out and group call, viz. one-to-many call manner is supported. Thus, it not only develops the services of cellular communication systems, but also debarrasses the private dispatching communication system from its limit in function and area.
As a professional trunking system, the most important difference from the traditional cellular communication lies in its high capacity and quick access. In a CDMA cellular system, the called user is paged by a manner of time slot. After the handset is power on, a time slot is calculated in accordance with IMSI to monitor a paging channel; when the system is to page a user, also a time slot (which is the same as the time slot for the monitor of the system terminal) is calculated in accordance with IMSI of said user, and a paging message is sent on said time slot, so that paging to the user is carried out. The smallest paging time slot cycle in existing CDMA systems is 0 (viz. 1.28 seconds), which leads to conceivable long paging time for some users and is far from meeting the requirement of quick access of the trunking system. Although a concept of the minus time slot is suggested in IS2000 R1sD protocol, it is merely corresponding to common voice call and simultaneously without support from trunking terminals or systems. Thus, the minus time slot paging cycle needs to be supported in the trunking system, so as to shorten the paging time of a trunking call and meet the requirements of trunking.
Furthermore, during used in existing R1s0 or R1sA systems, the minus time slot paging cycle should not only be usable in existing trunking terminals but also be usable in old trunking terminals. Furthermore, common voice calls and trunking functions of other trunking terminals not supporting the minus time slot should not be influenced. However, the paging time slot in the prior art is synchronized from trunking terminals to the system and cannot carry out compatibility of the old trunking terminals. Hence, the synchronizing mode needs to be changed to realize compatibility of all the trunking terminals.